In a separate pan, brown your lamb chunks in 2 tbsp oil and butter – season with 1 Tbspn salt and 1 tbsp pepper. Do not overcrowd so do this in 2 batches if you need to.
At the same time as you brown your lamb chunks, turn on your Instant Pot to Sauté mode and add 1 tbsp oil with onions. Sauté until translucent.
Add tomatoes to onions.
Once your meat is browned, add it to the Instant Pot.
Add dry wine and beef stock.
Place the lid on the Instant Pot and set it to high pressure for 40 minutes. During this time, peel your potatoes.
Quick-release when Instant Pot high pressure is done.
Add potatoes and olives. At this time taste to see if you need more salt/pepper. Add salt/pepper if you would like.
Place the lid on the Instant Pot and set it to high pressure for 4-5 minutes.
Quick-release when Instant Pot is done. Add 1 tbsp of corn starch (mix with a bit of cold water). This is optional if you want your stew to be thicker.